The present invention relates to a method of transferring ophthalmic lenses between treatment stations during manufacturing. Also disclosed and claimed are trays useful for transporting the lenses between stations. Included in this invention is a transfer tray for holding small, delicate articles such as contact lenses or intraocular lenses, a surface treatment support tray useful during gaseous processes, and a device for transferring the lenses from the transfer tray to the surface treatment support tray. In a preferred embodiment, contact lenses are transferred from a concave-side up position on the transfer tray to a concave-side down position on the surface treatment tray or vice-versa. The lenses are further subjected to a plasma reaction while on the surface treatment tray. The lenses may then be transferred using the inventive transfer tray for further processing such as polymer coating, extraction, hydration, or packaging, for example.
Those skilled in the art have long recognized the need for modifying the surface of hydrophobic contact lenses so that they are compatible with the eye. It is known that increased hydrophilicity of the contact lens surface improves the wettability of the contact lenses. This, in turn, is associated with improved wear comfort of contact lenses. Additionally, the surface of the lens can affect the lens susceptibility to deposition, particularly protein and lipid deposition from the tear fluid during lens wear. Accumulated deposition can cause eye discomfort or even inflammation. In the case of extended wear lenses, the surface is especially important since extended wear lenses must be designed for high standards of comfort over an extended period of time, without requiring daily removal of the lens before sleep. Thus, the regimen for the use of extended wear lenses would not provide a daily period of time for the eye to recover from any discomfort or other possible adverse effects of lens wear.
The patent literature has disclosed various surface treatments for rendering the surface of hydrophobic contact lenses, including those made with silicone materials, more hydrophilic and more wettable, including changing the chemistry of the surface layer, coating the surface, and compounding the polymer with additives that subsequently diffuse to the surface.
Silicone lenses, in particular, have been subjected to plasma surface reaction to improve their surface properties, e.g., surfaces have been rendered more hydrophilic, deposit resistant, scratch resistant, and the like. Examples of common plasma surface reactions include subjecting the contact-lens surfaces to plasma of an inert gas or oxygen (see, for example, U.S. Pat. Nos. 4,055,378; 4,122,942; and 4,214,014); various hydrocarbon monomers (see, for example, U.S. Pat. No. 4,143,949); and combinations of oxidizing agents and hydrocarbons, e.g., water and ethanol (see, for example, WO 95/04609 and U.S. Pat. No 4,632,844). Sequential plasma surface treatments are also known such as those comprising a first reaction with a plasma of an inert gas or oxygen, followed by a hydrocarbon plasma (see, for example, U.S. Pat. Nos. 4,312,575 and 5,326,584).
Another type of chemical surface modification that has been disclosed in the patent literature involves the introduction of functional groups absent in the parent polymer by the grafting or immobilization of molecules, oligomers, or polymers onto a surface. Grafting or immobilization typically involves, first, the formation of a grafting site which may comprise the formation of a radical by means of chemical reactions, UV irradiation, ionizing radiation, plasma reaction, or the like. The next step is the reaction of the species to be grafted or immobilized with the active site. Surface grafting typically involves the propagation of the reaction to form an anchored chain, wherein competing solution and interfacial reactions occur. Surface crosslinking may occur.
Non-plasma techniques for forming a coating have been disclosed. For example, U.S. Pat. No. 3,814,051 to Lewison discloses vacuum bonding a uniform hydrophilic quartz surface to a contact lens by vaporizing quartz, namely silicon dioxide, within a high vacuum chamber. The coating of contact lenses by dipping, swabbing, spraying or other mechanical means has been disclosed in U.S. Pat. Nos. 3,637,416 and 3,708,416 to Misch et al. The latter patents disclose a chemical process in which a coupling film-forming organic silicon compound, a vinyl trichlorosilane, is applied to a silicone surface, followed by a silica or silica gel deposit formed by contact with a silicon halide such as tetrachlorosilane or with a silicic ester, more particularly a tetraalkoxysilane.
In all of the above treatments, it is important that the surface area of the object being treated be uniformly coated. In particular, lenses that undergo coating or surface treatment need to be supported on a fixture or device which allows the entire lens surface to be coated evenly as possible. One such device is disclosed in U.S. Pat. No. 5,874,127 (Winterton et al). In Winterton et al., the contact lens is supported by a plurality of point-contact support locations. The support locations are sufficient to support the lens to be treated but do not prevent uniform coating of the lens.
Another such device capable of supporting lenses during surface treatment is disclosed in U.S. patent application Ser. No. 60/163,208 entitled xe2x80x9cMESH TRAYxe2x80x9d (assigned to Bausch and Lomb Incorporated, the entire contents herewith incorporated by reference). This tray comprises a mesh insert which is supported by a rigid, preferably metal tray. Plasma or any gaseous atmosphere may circulate within the mesh insert to uniformly coat the lens.
Material handling devices are known in the field of contact lens manufacturing. For instance, as shown in FIGS. 1-3 (prior art), a perforated tray assembly is used to transport mold assemblies between stations after casting (tray assembly 1 holding mold assemblies 5 shown in FIG. 3). The tray assembly has top portion 2 and base portion 4. Top portion 2 has a series of openings 2a which when assembled, rest on the lower portion 6a of upper mold 6. Base portion 4 also has a series of openings 4a but the openings are smaller than openings 2a and have a counterbore area 4b to correspond to outer diameter 7a of lower mold 7. Mold assembly 5 has upper mold portion 6 and lower mold portion 7. When assembled, mold assembly 5 rests on lower tray portion 4 and is secured in place by top tray portion 2. The upper mold portion 6 protrudes through opening 2a of top tray portion 2. This perforated tray assembly 1 allows mold assembly 5 to remain coupled while mold assembly 5 is transferred between stations.
Lenses are removed from the mold and edged, if necessary. The lenses are now ready for additional processes such as coating or surface treatment.
As previously mentioned, plasma reaction is a common surface treatment and has typically been a two-staged process.
In one prior art method, contact lenses requiring surface treatment are dry-released from the anterior mold and edged polished, if necessary. The lenses are placed manually by a worker concave-side up into a transfer tray. The transfer tray contains a plurality of cylindrical cavities with flat bottoms and is typically made from white polystyrene having a matte finish. The lens diameter is typically smaller than the diameter of the cavity so that the lens is easily placed and retrieved from the tray. The lenses are taken to a different workstation for surface treatment. At the surface treatment station (e.g. using commercial Metroline Plasma Deposition Model Number 7100 Series Chamber), lenses are inverted onto a surface treatment tray such as the removable shelf supplied with the Metroline Plasma Chamber. The Metroline shelf has a plurality of small, spaced perforations located at predetermined intervals, each of the perforations having diameters substantially smaller than any one of the lenses. Each lens is placed on the shelf, concave-side down. The lenses are plasma reacted and inverted, e.g. using a manual method or using a semi-automated device such as an air knife as disclosed in U.S. Pat. No. 5,503,515 (Moorehead, assigned to Bausch and Lomb Incorporated). Unfortunately, it has been found that when lenses are initially inverted from the transfer tray onto the Metroline shelf, placement of the lenses is random with the individual lens not necessarily over a perforation as intended. If an individual lens is not situated over a perforation, the lens will not invert. Instead, a worker must use tweezers to turn the lens over. The other side of the lens is then subjected to a plasma reaction. The surface treatment requires two cycles of plasma reaction. The lenses are then picked up by a worker using tweezers and transferred for other processing such as extraction. The worker is integral to this whole process, especially in making sure all the lenses invert over the air knife and transferring the surface treated lenses for extraction.
Small, delicate work pieces such as contact lenses are difficult to transfer. In the dry state, a contact lens is fragile and prone to scratching, cracking and breaking. Manipulating a contact lens into a desired orientation, such as having the concave side of the lens facing upward or toward a particular direction, can be difficult. The lens is extremely lightweight and can accumulate static charge. Usually, this lens is manually manipulated. A worker may have to turn the lens with a pair of tweezers. Inevitably, a few lenses are damaged by the tweezers or the worker is exposed to repetitive motions, contributing to injuries. It has therefore been desirable to automate as much of the contact lens manufacturing process as possible.
The present invention is directed to a method of handling and transferring small, delicate articles such as ophthalmic lenses between stations and during certain manufacturing process such as coating/plasma reaction processes. In particular, this invention provides a method of inverting lenses to place the lenses in correct position for surface treatment. The invention also discloses devices in the form of trays for supporting the lenses during processing and surface treatment. In particular, one device allows for a single cycle surface treatment when previously, two cycles were necessary.
In the first aspect, the present invention is directed to a transfer tray for containing lenses during movement from workstation to workstation. After the lenses are released from the mold assembly and if necessary, edged, they are placed onto a transfer tray concave-side up. The transfer tray is rigid and has numerous cavities formed for containing the lenses.
The transfer tray is then secured within a holding frame of an inverting device. The inverting device causes the transfer tray to rotate around an axis such that the tray, containing the lenses, is essentially inverted. The lenses are now concave-side down and resting on a surface treatment support tray,
The surface treatment support tray allows for unrestricted surface access in any gaseous type of surface treatment.
The surface treatment support tray is rigid and has a plurality of through-holes formed therein. On one surface of the tray is a shallow counterbore ring around each through-hole. The counterbore ring is slightly larger than the outer perimeter of a contact lens or intraocular lens while the through-hole is slightly smaller than the diameter of the lens. There is no masking of any portion of the lens surface.
In yet a further aspect of the invention, support trays may be affixed onto a larger tray such that multiple support trays are processed at one time. Examples of suitable larger trays include those used in plasma reaction chambers.
Advantages of the present invention include the reduced demand on a worker including less manipulation and handling of the lenses with tweezers which frequently destroy lenses which then must be scrapped. The inverting process is more precise, resulting in placement of the lenses in correct orientation and spacing into the next tray. The placement of the lenses is always precise and does not require the use of an air knife such as that disclosed in Moorehead. The surface treatment process can furthermore be performed in a single-cycle as opposed to a two-cycle process, reducing the time necessary for treating the lenses. Additionally, the lenses are directly transferred from a surface treatment tray into an apparatus for extraction.